The present invention relates to a thermal transfer medium which comprises a film made essentially of polytetramethyleneadipamide, as a supporting material. The thermal transfer medium does not melt by the heat of a thermal head, and it has excellent properties to prevent sticking to the thermal head. Thermal transfer media find application as typewriter ribbons and other fast printing devices.
For thermal transfer recording, a thermal transfer medium having a heat-meltable ink layer or heat-sublimable ink layer on one side of a polyester film or condenser paper has been used in many cases. The supporting material is heated from the side opposite to the ink layer to transfer the ink to a paper. This conventional method, particularly when a polyester film is used, shows the drawback that the polyester film due to its low heat resistance tends to melt partially by the heat of the thermal head, which at some instances reaches a level as high as about 400.degree. C. This tendency is particularly observed when a heat-sublimable ink is used, since in that case it is necessary to raise the temperature of the thermal head and to prolong the treating time due to the increased energy requirement for sublimation. Further, even if the film does not melt, the contact surface of the supporting material with the thermal head is partially softened and the slip properties tend to deteriorate. A so-called stick phenomenon is likely to occur in that case.
In order to solve these problems, for example, in many cases, a heat-resistant slippery coating is applied on the surface of the supporting material which faces the thermal head as disclosed in Japanese Examined Patent Publication No. 13359/1983. However, it is impossible to avoid the increase of the cost. Further, there remain several problems such as the heat resistant coating layer tending to peel from the supporting material.
The present inventors have conducted extensive research to solve these problems and, as a result, have invented the following thermal transfer medium.